1. Field of the Invention
The invention relates to an exhaust gas turbocharger for an internal combustion engine.
2. Prior Art
An exhaust gas turbocharger having an exhaust gas turbine to be driven by the exhaust gases of an internal combustion engine as well as a compressor in the intake tract is described in the reference DE 199 55 508 C1; its compressor wheel is driven by the turbine wheel, by way of a shaft. Combustion air is to be supplied to the compressor wheel by way of a compressor inflow channel, under atmospheric pressure, which air is compressed to an elevated charging pressure by way of the rotational movement of the compressor wheel; the combustion air is supplied to the cylinders of the internal combustion engine at this charging pressure.
The compressor has an additional channel that extends approximately parallel to the compressor wheel inflow channel and opens radially into the compressor wheel inflow channel in the vicinity of the compressor wheel. Combustion air can also be supplied via the additional channel. An adjustable guide grid is disposed in the orifice region into the compressor wheel inflow channel, which grid is adjustable between a blocked position that minimizes the orifice cross-section, and a release position that maximally opens the cross-section. Furthermore, a throttle valve is disposed in the compressor wheel inflow channel, upstream from the orifice of the additional channel into the compressor wheel inflow channel, by way of which the air mass stream to be supplied, through the compressor wheel inflow channel, can be adjusted.
In order to minimize the rpm spread of the exhaust gas turbocharger and also in order to be able to maintain a noteworthy rpm level of the charger even in operating states of low load and speed of rotation of the internal combustion engine, the compressor can also be used in turbine operation. For this purpose, the throttle valve in the compressor wheel inflow channel is adjusted to its closed position, and the combustion air is guided radially onto the vanes of the compressor wheel, by way of the additional channel, which wheel thereupon experiences a rotational impulse for additional power. Relaxation of the supplied combustion air is achieved by way of the compressor wheel, so that a desired partial vacuum can be implemented in the air inlet of the internal combustion engine, at a partial load of the internal combustion engine. In this manner, the charger is kept in rotation, which makes it possible to thereby clearly improve the transient behavior of the exhaust gas turbocharger. The transition to compressor operation with an increasing load can be performed within a shorter period of time.